PET Monofilament Loop Toughness via Annealing
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Solution Overview
Problem
Poly(ethylene terephthalate) (PET) monofilaments used in industrial applications often suffer from brittle failure under high loads, leading to loop breakage and low toughness, which limits their suitability as load-bearing yarns in industrial fabrics.
Innovation Solution
A process involving extrusion, quenching, multiple stages of stretching in a heat transfer medium, and relaxing of PET monofilaments to achieve high loop and tensile toughness, tenacity, and crystallinity, resulting in monofilaments with improved mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high stretching and high temperature annealing processes are used to improve tensile strength and modulus, then the mechanical strength properties are improved, but the filaments exhibit brittle failure mode and low loop toughness
Solution Approach 1:
The patent applies parameter changes by modifying the annealing temperature (reducing from high temperature to below the glass transition temperature), changing the annealing atmosphere (introducing liquid nitrogen environment), and adjusting the annealing time to achieve optimal balance between strength and toughness. This resolves the contradiction by finding a new parameter space where both tensile strength and loop toughness are improved
Solution Approach 2:
The patent creates a composite microstructure within the filament by forming a skin-core structure during the annealing process, where the skin layer and core layer have different crystalline orientations and properties. This composite structure allows the skin to provide strength while the core maintains toughness, resolving the brittle failure issue
2Productivity
If the filament diameter is increased to reduce the number of filaments needed, then the processing efficiency is improved, but the loop toughness deteriorates due to skin-core structure effects
Solution Approach 1:
The patent changes the critical parameter of filament diameter to fall within the optimal range of 0.05-0.15mm, where the skin-core structure effects are minimized. This parameter optimization allows larger filament sizes for better productivity while maintaining high loop toughness by staying within the critical diameter range where bending stress differences between skin and center are reduced
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process enhances the loop toughness to at least 1.3 gf/den and tensile toughness to at least 0.9 gf/den, making PET monofilaments suitable for demanding industrial applications such as paper machine fabrics by minimizing microstructure defects and optimizing crystallinity.
Implementation Method 1
stretching of the extrudate in a heat transfer medium
Implementation Method 2
quenching the extrudate
Data Source
AI summary
Poly(ethylene terephthalate) monofilaments having improved loop strength and toughness as well as improved tensile strength and tensile toughness. The yarns can have a loop toughness of at least 2 gf/den, a loop tenacity of at least 7 gf/den, a tensile toughness of at least 0.9 gf/den, a tensile tenacity of at least 4 gf/den, and a DSC crystallinity of at least 35%. A process for the production of poly(ethylene terephthalate) monofilaments includes melt extrusion, orientation of the extrudates by stretching, and further stretching as well as heat treating the stretched monofilaments. Industrial fabrics, especially fabrics for paper machine clothing, can be made of such monofilaments as load bearing yarns that resist loop failure and that resist fabric creep at high temperature and high load.